1. Field of the Invention
The present invention relates to an organic light emitting display device (OLED) and method of fabricating the same and, more particularly, to an easily fabricated organic light emitting display device having uniform display characteristics and method of fabricating the same.
2. Description of the Related Art
Active and passive matrix OLEDs incorporate thin film transistors and have attracted attention in recent years as providing an alternative to cathode ray tube (CRT) devices because OLEDs offer wider viewing angle, better contrast, and faster response speed.
OLEDs may be classified as organic or inorganic depending on the type of electroluminescent (EL) material used to form the emission layer of each pixel. The organic EL device has advantages of excellent luminance, low driving voltage, fast response speed, and realization of multi-colors, as compared to an inorganic EL device.
Further, an organic light emitting display device may comprise a full-color flat panel display device by implementing red, green, and blue colors on respective pixel regions, which are defined by a plurality of scan lines and a plurality of data lines that are formed perpendicular to the scan lines.
FIG. 1 is a cross-sectional view of a conventional full-color organic light emitting display device 1. In the conventional organic EL device 1, first electrode layers 12 are each formed in a predetermined pattern on a substrate 10 having red, green and blue color pixel regions to emit red, green and blue colors R, G, and B. In a top-emission organic light emitting display device, each of the first electrode layers 12 is formed of a reflective material such as metal, or is formed of a transparent material backed with a layer of reflective material.
An insulating material is deposited in the gaps between electrode layers 12 to form a pixel defining layer 14, which is then patterned to form an opening above each electrode layer 12. In this manner, the insulating material separates the respective pixel regions to define individual pixels.
The hole injection layer 16 may be covered with a hole transport layer 18 to create a common layer over the entire surface of the substrate that encapsulates the first electrode layers 12.
Subsequently, light emitting materials corresponding to the respective pixel regions may be deposited on the hole transport layer 18 to form red, green, and blue emission layers 20.
A hole blocking layer (not shown), an electron transport layer (not shown), and an electron injection layer 22 are sequentially formed over the entire surface of the substrate. A second electrode layer (not shown) having a pre-determined pattern may be formed on the electron injection layer 22, if necessary. The hole injection layer 16, the hole transport layer 18, the emission layer 20, the hole blocking layer, the electron transport layer, and the electron injection layer 22 may be organic thin films made of an organic compound.
However, in the full-color organic light emitting display device 1, there arises a difference in luminous efficiency between the differently colored pixels. That is, a red-colored light-emitting material has superior luminous efficiency as compared to green-colored and blue-colored light-emitting materials. Additionally, the green-colored light-emitting material has superior luminous efficiency to the blue-colored light-emitting material.
Accordingly, there have been many conventional attempts to control the thickness of organic thin films in order to obtain maximum efficiency and luminance. For example, Japanese Patent Laid-open No. Hei 4-137485 discloses a technique in which, in a configuration having an anode, a hole transport layer, an emission layer, an electron transport layer and a cathode formed in sequence, the thickness of the electron transport layer is set to about 30 nm to about 60 nm to enhance the luminous efficiency.
Further, Japanese Patent Laid-open No. Hei 4-328295 discloses a technique in which the thickness of an electron transport layer is adjusted so that the luminance substantially increases when light emitted from an emission layer and light reflected by a cathode interfere therewith. Further, Japanese Patent Laid-open No. Hei 7-240277 discloses an organic light emitting display device in which optical film thickness is controlled to improve luminance, in particular, to increase color purity of blue-color emission.
In these organic light emitting display devices, a different optical thickness is set for each color to improve the luminance. However, it is difficult to make the optical thickness different for each color in mass production because each color requires a different manufacturing process or step.